Attachment plate for top-tightening clamp assembly in a spinal fixation system

ABSTRACT

An attachment plate for use with a spinal rod system converts a normally side-tightening eyebolt to a top-tightenable arrangement for engaging spinal fixation elements to the spinal rod. The plate is configured for use with spinal fixation elements having a posteriorly projecting central post, one lateral surface of the post contacting the spinal rod when the rod extends through an aperture of the eyebolt. The attachment plate is generally L-shaped with a slot in one portion for receiving the posteriorly projecting threaded post of the eyebolt. The plate includes a flange portion having a surface configured to engage the lateral surface of the fixation element post opposite the spinal rod. The attachment plate includes a camming segment to provide a clamping force component directed toward the flange portion of the plate to thereby tightly clamp the spinal rod to the fixation element post when a nut is threaded onto the eyebolt threaded post.

BACKGROUND OF THE INVENTION

The present invention concerns spinal fixation systems, and particularlysystems utilizing elongated rods adjacent the spinous process providinga base for connecting fixation elements to several vertebral levels.More specifically, the invention concerns improvements to the manner inwhich the vertebral fixation elements, such as spinal hooks and bonescrews, are engaged to the elongated spinal rod.

Several techniques and systems have been developed for correctingstabilizing spinal curves and facilitating spinal fusion. In one system,a bendable rod is longitudinally disposed adjacent the vertebral column,or spinous process, and is fixed to various vertebrae along the lengthof the column by way of a number of fixation elements. A variety offixation elements can be provided which are configured to engagespecific portions of the vertebra. For instance, one such fixationelement is a spinal compression/distraction hook. This type of spinalhook is used to anchor the rod typically by engaging the laminae of thevertebra. Another fixation element is a spinal screw, which includescancellous threads for engagement within the pedicle of a vertebra.

An example of a rod-type spinal fixation system under consideration withthe present invention is the TSRH® spinal system sold by Danek Medical,Inc. In this system, a spinal hook, such as the hook H shown in FIG. 1for example, is engaged to an elongated fixation rod R by way of aneyebolt assembly E. As is known in the art, the eyebolt E is mounted onthe spinal rod and captured within yokes on the spinal hook. A nut N isthen threaded onto a threaded post of the eyebolt to clamp the hook yokebetween the nut and the fixation rod R. In this manner, the eyebolt Eand yokes of the hook H provide three degrees of fixation as representedby the arrows in FIG. 1. Details of the TSRH® spinal implant system aredisclosed in the "TSRH® Surgical Technique Manual provided by DanekMedical, Inc., published in 1990, which disclosure is incorporatedherein by reference.

It is the goal of the surgeon using spinal implant systems such as theDanek TSRH® system to apply vertebral fixation elements, such as aspinal hook or a bone screw, to the spine in appropriate anatomicpositions, and then to engage each fixation element to the spinal rod.One problem with the spinal hooks H of the prior art, as represented inFIGS. 1 and 2, is that the hooks are rather bulky and wide since thefixation yokes of the hook are configured to surround the spinal rod R.Moreover it had been found that hooks of this type only allow the rod tobe implanted in one position relative to the spinal column as dictatedby the required position of the shoe of the hook against the vertebra.

In order to address that and other problems with the prior art systemsshown in FIGS. 1 and 2, new spinal fixation elements have been developedwhich are the subject of pending applications assigned to the assigneeof the present invention. One such fixation element, a spinal hook 10shown in FIGS. 3 and 4, includes a shoe 11 having a bone engagingsurface 12. The bone engaging surface 12 can be formed in any knownshape to engage a laminae of a vertebra, for instance. Integral with theshoe 11 is a top portion 13 that forms a pair of posts 14 disposed apartfrom each other in the form of a U-shaped yoke to define a slot 15therebetween. The slot 15 is wide enough to receive an eyebolt assemblytherein, such as eyebolt assembly E shown in FIGS. 1 and 2. A pair ofcoaxial grooves 16 are formed in each lateral surface 18 of the hook 10to receive a portion of a spinal rod, such as rod R shown in FIGS. 1 and2. These rod grooves 16 are present on each opposite lateral surface 18of the posts 14 so that the hook 10 can be oriented on either side of aspinal rod. Slots 17 are provided each end face 19 for engagement by ahook-holding insertion instrument.

The upper portion 13 and posts 14 can be referred to as a "central post"configuration of fixation element 10. A similar central postconfiguration can be utilized with fixation elements other than hooks,such as bone bolts or screws. Leaving the details of the newly developedcentral post vertebral fixation elements to its pending application, itcan be appreciated that the central post hook 10, of FIGS. 3 and 4, hasincreased the versatility of rod-type spinal implant systems, such asthe TSRH® system provided by Danek Medical. However, one featureconsistent between this hook 10 and the prior art spinal hook H shown inFIG. 1, is that the eyebolt assembly E used to engage the fixationcomponent to the spinal rod is "side-tightening". In other words, thethreaded post of the eyebolt E and the nut N engaging the post bothproject laterally away from the spinal rod R when implanted in apatient, as specifically depicted in FIGS. 1 and 2. It has been found inpractice that it is often cumbersome to engage the nut N with a wrenchto tighten the nut onto the laterally projecting posts of the eyeboltassembly E. Moreover, space limitations at the implant site dictate thatthe wrench can only be moved through a partial turn before the handle ofthe wrench contacts the surrounding tissue. This necessitates taking thewrench off of the nut and re-engaging it for an additional partialrotation. Ratchet type wrench systems are typically not acceptable inprocedures of this sort due to the risk of trauma to the surroundingtissue and the greater lateral clearance required to receive the ratchetmechanism at the surgical site.

In many procedures, it is desirable to utilize an eyebolt assembly,comprising the eyebolt E and nut N, for engaging the fixation elementsto the spinal rod. These eyebolts are very convenient to the surgeon andare relatively easy and inexpensive to produce. One particular advantageof utilizing the eyebolt to engage the fixation element to the rod isthe ability to provide a three-point clamp between the top portion 13 ofthe fixation element 10 and the rod R. This three-point clamp restrictsrelative movement between these two components in all six degrees offreedom so that a rigid construct can be formed. While there areadvantages to retaining the eyebolt assembly approach to correcting thefixation element to the rod, the prevailing disadvantage of theside-tightening aspect of this approach frequently makes use of aneyebolt assembly cumbersome.

Spinal and orthopaedic procedures are rapidly becoming prevalentsurgeries, largely because of the high incidence of low back painsyndrome. In the past, surgical techniques for alleviating low back painor for addressing spinal deformities or injuries has required fairlycomplicated and massive surgical techniques. The focus in recent timeshas been to greatly reduce the degree of invasion into the patientrequired for instrumenting a spine, as well as to reduce the amount oftrauma to tissue surrounding the instrumentation, both during theprocedure and after the spinal instrumentation has been implanted.

One cog in this worthwhile goal for minimally invasive spinal surgicaltechniques, is to provide an improved means for clamping the variousvertebral fixation components to a spinal rod in a patient. Such asystem should eliminate the side-tightening requirement of prior artsystems to thereby minimize the intrusion into the patient. In addition,such a system should retain the versatility achieved by newly developedcentral post fixation elements. It is the goal of the present inventionto address this and other concerns.

SUMMARY OF THE INVENTION

In accordance with the invention, an attachment plate is provided foruse with a spinal rod system to convert a normally side-tighteningeyebolt to a top-tightenable arrangement for engaging spinal fixationelements to the spinal rod. The plate is configured for use with spinalfixation elements having a posteriorly projecting central post, onelateral surface of the post contacting the spinal rod when the rodextends through an aperture of the eyebolt. An eyebolt assembly is usedto engage the fixation element to the spinal rod, which assemblyincludes an eyebolt body having an aperture for receiving the spinal rodand a threaded post projecting from the body to receive a nut threadedthereon.

In the preferred embodiments of the invention, the attachment plate isgenerally L-shaped with a slot in an eyebolt engaging portion forreceiving the threaded post of the eyebolt. The plate further includesan anteriorly projecting clamping portion configured for engaging thefixation element post. The clamping portion includes a flange portionhaving a surface configured to engage the lateral surface of thefixation element post opposite the spinal rod.

The attachment plate includes a segment performing a camming function toprovide a clamping force component directed toward the flange portion ofthe plate to thereby tightly clamp the spinal rod to the fixationelement post when a nut is threaded onto the eyebolt threaded post. Inone embodiment, the plate includes a lower surface with a cam portionoriented to contact the spinal rod with the attachment plate disposedbetween the rod and the eyebolt assembly nut. The cam portion isconfigured to urge the spinal rod toward the flange portion of theattachment plate as the eyebolt nut is tightened down on the eyeboltpost against the upper surface of the attachment plate. In this manner,the eyebolt nut is top-tightenable, that is, accessible posteriorly whenthe system is implanted adjacent a patient's spine.

In another embodiment, the eyebolt engaging portion is generally a flatplate that includes a sloped recess in its upper surface adjacent theeyebolt nut. The recess is sloped toward the flange portion of theattachment plate. The eyebolt nut includes a spherical surface which isreceived within the recess in the attachment plate. As the nut istightened down on the eyebolt post and against the attachment plate, thespherical nut surface advances down the sloped recess to its finalseating position. Movement of the nut down the sloped recess forces theeyebolt closer to the fixation element post so that the spinal rod isclamped between the aperture of the eyebolt and the surface of thefixation element post.

The attachment plate provides means for converting an otherwiseside-tightened eyebolt to a top-tightenable eyebolt, thereby greatlyfacilitating connection of spinal fixation elements to a spinal rod. Ina typical fixation rod procedure, the spinal fixation element, such as aspinal hook, is engaged to a vertebra with its post projectingposteriorly. The spinal rod is disposed within the patient adjacent thepost or the fixation element. An eyebolt is threaded onto the rod and isarranged on the rod adjacent the fixation element post with the eyeboltthreaded post also projecting posteriorly. The attachment plate is theninstalled with the flange portion being first placed in contact with thepost of the fixation element. The attachment plate is then pivotedanteriorly until the eyebolt engaging portion of the plate is alignedlaterally across the spinal rod and eyebolt body with the eyeboltthreaded post extending through the slot in the attachment plate. Theeyebolt nut is then threaded onto the eyebolt threaded post until itcontacts the attachment plate eyebolt engaging portion. The cammingsegments of the attachment plate urge the spinal rod into firm contactwith the fixation element post as the nut is tightened further downagainst the attachment plate.

The attachment plate of the present invention provides a significantbenefit in that it permits the use of eyebolts to engage fixationelements to a spinal rod, while providing means to allow top-tighteningor the eyebolt nuts. Prior systems rely upon access to the nuts lateralto the components, or side-tightening. The present attachment plateallows the eyebolt to be rotated on the spinal rod so that the threadedeyebolt post is projecting posteriorly to a more readily accessibleposition for the surgeon. Further, tightening the eyebolt nut againstthe attachment plate increases the clamping force of the rod to thefixation element to produce a rigid construct.

It is then one object of the present invention to provide a system thatcan be used with existing spinal rod and eyebolt attachment systems toconvert the eyebolts from a side-tightening to a top-tighteningconfiguration. Another object is to provide an easily implanted andmanipulated component at the surgical site that will streamline theimplant procedure and reduce the amount of trauma suffered by thesurrounding tissue over prior systems.

A further object of the present invention is to provide a component thatenhances the clamping force between the spinal rod and the fixationelement to form a rigid construct. Other objects and certain benefits ofthe present invention will become apparent from the following writtendescription read in combination with the accompanying figures.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a spinal hook of known design engaged to a fixation rod byway of an eyebolt assembly, as configured in accordance with one priorart system, the TSRH® spinal system.

FIG. 2 is a side view showing the prior art system depicted in FIG. 1 inwhich a standard fixation hook is engaged about the laminae of a lumbarvertebra.

FIG. 3 is a side elevational view of the spinal hook of recent designfor which the top-tightening clamp assembly of the present invention isconfigured to engage.

FIG. 4 is an end elevational view of the spinal hook shown in FIG. 3.

FIG. 5 is a side elevational view of the attachment plate assembly inaccordance with one embodiment of the present invention, shown clampinga spinal hook of the type shown in FIG. 4 to a spinal rod.

FIG. 6 is a top elevational view of the attachment plate shown in FIG.5.

FIG. 7 is a side elevational view of an alternative embodiment of theattachment plate in accordance with the present invention.

FIG. 8 is a top elevational view of the attachment plate shown in FIG.7.

FIG. 9 is an end cross-sectional view of the attachment plate shown inFIG. 8 taken along line 9--9 as viewed in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, such alterations and furthermodifications in the illustrated device, and such further applicationsof the principles of the invention as illustrated therein beingcontemplated as would normally occur to one skilled in the art to whichthe invention relates.

As discussed in the background of the invention, the present inventioncontemplates a system for engaging a vertebral fixation element to aspinal rod. More particularly, the fixation element is configured asshown in FIGS. 3 and 4 having a top portion 13 that forms a pair ofposts 14 defining a slot 15 therebetween in a "central post"configuration. It is understood that although in the specificembodiments disclosed herein the fixation element is a spinal hook, thesame "central post" approach can be applied to other types of vertebralfixation components, such as a bone screw. Whether the fixation elementis a hook or a screw, it is engaged with the vertebra first and thenclamped to the spinal rod using an eyebolt assembly.

In accordance with the present invention, an attachment plate 25 isprovided which includes an eyebolt engaging portion 27 and a fixationelement clamping portion 29. An eyebolt assembly 30 is provided which ismodified somewhat from the eyebolt E shown in FIG. 1. In particular, theeyebolt assembly 30 includes an eyebolt body 31 having a centralaperture 32 therethrough for receiving a spinal rod R therethrough. Athreaded post 33 projects from a surface of the eyebolt body 31. Thepost 33 is adapted to engage a machine threaded nut 34 in a knownmanner. A central difference between this eyebolt assembly 30 and othermore conventional eyebolts is that the threaded post 33 is longer sothat it can receive the attachment plate 25 thereon.

In one preferred embodiment, the attachment plate 25, and particularlythe eyebolt engaging portion 27 is forked, as shown in FIG. 6.Specifically, the eyebolt engaging portion includes a pair of arms 36which define a slot 37 therebetween. The slot 37 is wide enough toreceive at least the threaded post 33 of the eyebolt assembly 30therethrough. The eyebolt engaging portion 27 also includes an uppersurface 38 against which the eyebolt nut 34 is threaded. The width ofslot 37 cannot exceed the flat width of the nut 34 and is preferablysufficiently narrower than the nut to provide solid purchase against theupper surface 38 when the nut is tightened thereon.

In the specific embodiment shown in FIG. 5, the eyebolt engaging portion27 further includes a lower rod engaging surface 40. This rod engagingsurface is formed on each of the arms 36 and is preferably curved toaccommodate the spinal rod R, and to operate as a cam surface asdescribed herein. In one specific embodiment, the lower rod engagingsurface 40 spans about one-fifth of the circumference of the spinal rod.Most of the rod engaging surface 40 contacts the spinal rod R at aposterior surface 41_(P) (as viewed when engaged within the patient),and further includes a segment lateral to the spinal rod, which segmentis designated 41_(L) in FIG. 5. As will be explained more fully herein,the rod engaging surface, and particularly the lateral segment 41_(L),acts as a camming surface to provides a firm clamping force against thespinal rod R.

The attachment plate 25 further includes a fixation element clampingportion 29 which is more particularly defined by an anterior projectingflange 43. The end of the flange 43 is formed into a projection 45 whichis configured to engage the coaxial grooves 16 in one lateral surface 18of the fixation element 10. In the specific embodiment of FIG. 5, thisprojection 45 has a curvature substantially identical to the curvatureof the coaxial grooves 16 so that the projection will fit snuggly withinthe grooves when the assembly is completed. The attachment plate 25includes insertion instrument slots 47 in the eyebolt engaging portion,and particularly in opposite faces of the arms 36. As with the fixationelement, the instrument holding slots 47 provide a means for the plateto be held by an insertion instrument during the instrumentationprocedure.

From the foregoing description of the attachment plate 25 and itsrelation to the fixation element and rod, the manner of use of the plateshould be readily apparent. It is contemplated with use of the presentinvention that the surgeon would have already positioned variousfixation elements, such as hook 10, at appropriate vertebral levels. Aproperly positioned fixation element will have its top portion 13, andparticularly the central posts 14, projecting posteriorly. Severaleyebolt bodies 31 can be pre-threaded onto the spinal rod prior to itslocation adjacent the spine. As the spinal rod or the vertebral columnis manipulated to position the fixation elements in contact with thespinal rod R, each eyebolt body 31 is positioned between the posts 14 ofa corresponding fixation element 10 so that the rod R extending throughthe eyebolt aperture 32 contacts the coaxial grooves 16 on one side ofthe hook central posts 14. Further, the eyebolt body is situated so thatits threaded post 33 also projects posteriorly for easy access by thesurgeon.

With the threaded post 33 projecting posteriorly, the attachment plate25 is top-loaded over the eyebolt assembly 30 and in contact with thefixation element 10. More particularly, the attachment plate 25 isloaded so that the projection 45 first engages the coaxial groove 16 onthe side of the central posts 14 opposite the rod R engagement. Theattachment plate is then pivoted anteriorly so that the lower rodengaging surface 40 contacts the spinal rod R as it is situated directlyadjacent the fixation element 10. Some manipulation may be required tobring the rod R into contact with the fixation element 10, whilesimultaneously contacting the lower rod engaging surface 40 of theattachment plate 25. Preferably, the slot 37 defined between the arms 36is open at its end (as depicted in FIG. 6) to readily receive theeyebolt threaded post therein as the plate is pivoted anteriorly.Alternatively, the slot 37 can be closed at both ends. A closed slot 37increases the complexity of the installation of the plate by requiringthat the eyebolt assembly 30 be rotated about the rod R somewhat so thepost 33 is oriented at an angle. With the post 33 so oriented, the slot37 will slide over the post 33 when the plate is rotated. As the plate25 is rotated closer to the rod, the post 33 will also naturally rotateto its normal installed posterior facing position.

With the three components (fixation element 10, spinal rod R andattachment plate 25) in intimate contact, the nut 34 is threaded ontothe post 33 until it engages the posteriorly facing upper surface 38 ofthe attachment plate 25. As the nut 34 is threaded further and moretightly onto the eyebolt post 33, the fixation element top portion 13and spinal rod R are clamped between the projection 45 and the lower rodengaging surface 40 of the attachment plate 25.

It can thus be seen that the attachment plate 25 provides a ready meansfor converting an otherwise side loading eyebolt assembly into atop-loading eyebolt assembly for engaging a fixation element. The slot37 in the attachment plate 25 allows for easy manipulation of theeyebolt and spinal rod relative to the fixation element until finalclamping is desired. As the nut 34 is threaded onto the post 33 of theeyebolt assembly 30, the lower rod engaging surface 40, and particularlythe lateral segment 41_(L), acts as a camming surface to gradually urgethe spinal rod into a firmer engagement with the coaxial groove 16 onone lateral surface 18 of the fixation element 10. The lateral segment41_(L) provides a clamping force component directed toward the clampingportion flange 43 and particularly toward the projection 45.Simultaneously, the clamp engagement between the projection 45 andcoaxial groove 16 on the other side of the fixation element is alsoincreased.

As indicated, in the preferred embodiment the rod engaging surface 40,including the lateral segment 41_(L), is curved, preferably atapproximately the same radius as the spinal rod. Alternatively, thelateral segment 41_(L) can assume other configurations, provided that alateral clamping force component is exerted by the rod engaging surface40 against the spinal rod R. For example, a lateral segment 41_(L) thatis oriented at an angle relative to both the posterior and lateraldirections will provide such a clamping force component as the rod Rslides against the angled segment.

An alternative embodiment of the present invention is shown in FIGS. 7through 9. Specifically, an attachment plate 50 is shown which does notinclude the same lower rod engaging surface 40 as the attachment plate25 of FIG. 5. The attachment plate 50 does include an eyebolt engagingportion 52 and a fixation element clamping portion 53. The fixationelement clamping portion 53 also includes an anterior projecting flange55 terminating in a projection 56 which is configured to engage thecoaxial groove 16 in one lateral surface 18 of the fixation element 10.

As with the attachment plate 25, the plate 50 includes a pair of arms 59which define a slot 60 therebetween configured to receive the threadedpost 33 of the eyebolt assembly 30 therethrough. In this embodiment, theslot 60 is narrower than the eyebolt body 31 so the lower surface 61 ofthe plate 50 can contact the upper surface 35 of the eyebolt body.Further, instead of the camming action provided by the lower rodengaging surface 40 of the plate 25, the attachment plate 50 includes asloped recess 62 defined in the upper surface 63 of the eyebolt engagingportion 52. This sloped recess 62, or camming surface, is configured toengage a lower spherical surface 65 of a specially configured nut 66.

As can be seen more clearly in FIG. 7, the recess 62 slopes from end 62aat the open end of the arms 59 toward the portion 62b adjacent the innerend of the slot 60. In other words, the recess 62 slopes toward theanteriorly projecting flange 55 so that the eyebolt nut 66 is drawn inthat direction as it is tightened onto the threaded post. This slopedrecess 62 serves the same camming function as the lower rod engagingsurface 40 of the previous embodiment. More particularly, as the nut 66is threaded onto the post 33, the lower spherical surface 65 contactsthe sloped recess 62. As it is threaded further onto the threaded post33, the spherical surface 65 gradually slides down the sloped recess 62until it seats at the end portion 64 of recess 62 the attachment plate50. In effect, then the interaction between the lower spherical surface65 of the nut 66 and the sloped recess 62 of the attachment plate 50draws the threaded post 33 closer to the fixation element 10. Theeyebolt body 31 naturally follows with the threaded post 33 so that thebody too is forced closer to the fixation element central post 15. Inthis manner the spinal rod R is forced to contact the walls of theaperture 32 of the eyebolt body 31 generally lateral to the fixationelement 10 at the same time that the rod R contacts the groove 16 in theone surface of the fixation element post 15. The rod R is then clampedbetween the eyebolt and the fixation element 10, while the fixationelement 10, and more particularly the central post 14, is clampedbetween the projection 56 of the attachment plate and the spinal rod R.The plate itself is clamped between the upper surface 35 of the eyeboltbody and the nut 66. The attachment plate 50 is loaded and engaged tothe fixation components in a manner similar to that described inconnection with attachment plate 25 of the previous embodiment.

The attachment plates 25 and 50 are preferably formed of 316L stainlesssteel having a tensile strength of about 125 ksi. However, otherbiocompatible materials may be suitable for forming the attachmentplate. While the generally L-shaped configuration of the plates 25 and50 facilitate installation of the plates, this same shape can lead tostress concentrations at the intersection between the eyebolt engagingportion and the anterior projecting flange. The plates must be strongenough to withstand bending, particularly at the joint between theflange 43 and the eyebolt engaging portion, such as portion 27 of theplate 25. The internal and external comers at this joint between the twoportions are preferably rounded, as shown in FIGS. 5 and 7, to reducethe likelihood of stress concentrations forming at that intersection. Itis understood that this portion of the attachment plate 25 will endure asignificant amount of load as the entire assembly is tightened torigidly clamp the fixation element 10 to the spinal rod R.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiments have been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

What is claimed is:
 1. A spinal fixation system for implanting into thespine of a patient comprising:a spinal rod configured for positioningadjacent the spine: a vertebra fixation element, including;a vertebraengaging portion configured for engaging a vertebra of the spine; and arod engaging portion defined by a post having a pair of opposite lateralsurfaces, said post configured to project away from the vertebra whensaid vertebra engaging portion is engaging the vertebra; an eyeboltassembly including;an eyebolt body defining an aperture therethroughreceiving said spinal rod therein, and having a threaded post projectingfrom said body; and a threaded nut for engaging said threaded post; andan attachment plate, said plate including;an eyebolt engaging portiondefining a slot therethrough for receiving said threaded post thereinand having an upper surface for contacting said nut when said nut isthreaded onto said post; and a clamping portion for engaging saidfixation element, said clamping portion formed by a flange projectingfrom said upper surface of said plate and configured to contact one ofsaid pair of opposite lateral surfaces of said fixation element, whereinsaid rod contacts the other of said pair of lateral surfaces of saidfixation element when said rod extends through said aperture of saideyebolt body and when said threaded post of said eyebolt body projectsthrough said slot in said attachment plate, and further wherein said nutis tightenable along said threaded post against said upper surface ofsaid plate to thereby clamp together said clamping portion of saidplate, said post of said vertebra fixation element and said spinal rod.2. The spinal fixation system of claim 1, wherein said eyebolt engagingportion of said attachment plate includes a lower surface, opposite saidupper surface, contacting said rod when said rod extends through saidaperture of said eyebolt body and when said threaded post extendsthrough said slot so that said plate is clamped between said rod andsaid nut when said nut is threaded onto said post of said eyebolt. 3.The spinal fixation system of claim 2, wherein said lower surface ofsaid eyebolt engaging portion includes a cam segment arranged to providea clamping force component against said spinal rod directed toward saidclamping portion of said plate when said plate is positioned betweensaid eyebolt assembly nut and said spinal rod.
 4. The spinal fixationsystem of claim 3, wherein said cam segment of said lower surface ofsaid eyebolt engaging portion is curved to receive said spinal rodtherein.
 5. The spinal fixation system of claim 1, wherein:said eyeboltbody has an upper surface from which said threaded post projects, saidupper surface having a first width; and said eyebolt engaging portion ofsaid attachment plate includes;said slot defining a second width lessthan said first width: and a lower surface opposite said upper surfaceof said plate, whereby said attachment plate is clamped between saideyebolt body and said threaded nut with said nut contacting said uppersurface of said attachment plate and said eyebolt body upper surfacecontacting said lower surface of said eyebolt engaging portion.
 6. Thespinal fixation system of claim 5, wherein:said threaded nut includes aspherical surface; and said upper surface of said eyebolt engagingportion of said attachment plate defines a recess for receiving saidspherical surface of said nut when said nut is tightened against saidattachment plate.
 7. The spinal fixation system of claim 6, wherein saidrecess is sloped into said plate toward said flange so that as said nutis tightened onto said threaded post of said eyebolt assembly saidspherical surface slides along said sloped recess toward said flange. 8.The spinal fixation system of claim 1, wherein:each of said oppositelateral surfaces of said post of said fixation element includes a groovedefined therein configured to contact said spinal rod; and said flangeof said fixation element engaging portion of said attachment plateincludes a curved projection configured to be seated within a groove inone of said opposite lateral surfaces.
 9. The spinal fixation system ofclaim 1, wherein said eyebolt engaging portion includes a pair ofparallel arms, said arms defining said slot therebetween.
 10. Atop-loaded attachment plate assembly for use with a spinal fixationsystem that includes a spinal rod and a vertebra fixation element havinga vertebra engaging portion and a rod engaging portion with oppositesurfaces, one of the opposite surfaces contacting the spinal rod, saidattachment plate assembly comprising:an eyebolt assembly including;abody defining an aperture and a threaded post extending from said body,said aperture sized to receive the spinal rod therethrough; and a nutfor engagement with said threaded post; an attachment plate including;aneyebolt engaging portion defining a slot therethrough for receiving thethreaded post of the eyebolt therein and having an upper surface forcontacting the nut when the nut is threaded onto the post; and aclamping portion for engaging the fixation element, said clampingportion formed by a flange projecting generally perpendicularly fromsaid upper surface of said plate and configured to contact one of theopposite surfaces of the rod engaging portion of the fixation elementopposite the surface contacted by the spinal rod, wherein said flangeand said slot are arranged relative to each other to clamp the rodengaging portion of the vertebra fixation element between the spinal rodand said flange when the spinal rod extends through said eyeboltaperture and said eyebolt threaded post extends through said slot. 11.The top-loaded attachment plate assembly of claim 10, wherein saideyebolt engaging portion includes a lower surface, opposite said uppersurface, arranged to contact the spinal rod when the rod extends throughsaid aperture of said eyebolt body and when said threaded post extendsthrough said slot so that said plate is clamped between the rod and saidnut.
 12. The top-loaded attachment assembly plate of claim 11, whereinsaid lower surface of said eyebolt engaging portion includes a camsegment arranged to provide a clamping force component against thespinal rod directed toward said clamping portion of said plate when saidplate is positioned between the nut and the spinal rod.
 13. Thetop-loaded attachment plate assembly of claim 12, wherein said camsegment of said lower surface of said eyebolt engaging portion is curvedto receive the spinal rod therein.
 14. The top-loaded attachment plateassembly of claim 10, in which the eyebolt has an upper surface fromwhich the threaded post projects, the upper surface having a firstwidth, wherein said eyebolt engaging portion of said attachment plateincludes:said slot defining a second width less than said First width;and a lower surface opposite said upper surface of said eyebolt body,whereby said attachment plate is clamped between the eyebolt and the nutwith the nut contacting said upper surface of said plate and said lowersurface of said plate contacting the upper surface of the eyebolt. 15.The top-loaded attachment plate assembly of claim 14, in which thethreaded nut includes a spherical surface, wherein said upper surface ofsaid eyebolt engaging portion of said attachment plate defines a recessfor receiving the spherical surface of the nut when the nut is tightenedagainst said attachment plate.
 16. The top-loaded attachment plateassembly of claim 15, wherein said recess is sloped into said platetoward said flange so that as said nut is tightened onto said threadedpost of said eyebolt the spherical surface of the nut slides along saidsloped recess toward said flange.
 17. The top-loaded attachment plateassembly of claim 10, in which each of the opposite surfaces of the rodengaging portion of the fixation element includes a groove definedtherein configured to contact the spinal rod, wherein said flange ofsaid fixation element engaging portion of said attachment plate includesa curved projection configured to be seated within a groove in one ofsaid opposite surfaces.
 18. The top-loaded attachment plate assembly ofclaim 10, wherein said eyebolt engaging portion includes a pair ofparallel arms, said arms defining said slot therebetween.